This invention pertains generally to radio frequency oscillators and particularly to oscillators of such type which are adapted to combine the power out of a plurality of solid state devices.
It has been known for many years that radio frequency signals out of each one of a plurality of oscillatory circuits may, in effect, be added in so-called "combiner" circuits to produce a single radio frequency signal of high amplitude. With the development of solid state devices, such as IMPATT diodes, as the active elements in oscillatory circuits, the interest in combiner circuits has increased. The average and peak power levels of these devices are high enough so that useful transmitter power levels can be achieved by combining a practical number of devices in a suitable combiner circuit. Exemplary combiner circuits using solid state devices are shown in U.S. Pat. Nos. 3,628,171 (Kurokawa et al.) and 3,931,587 (Harp et al.).
Both of the just-cited patents show combiner circuits with a plurality of IMPATT diodes operated as continuous wave (CW) oscillators, each one of such diodes being in an oscillatory circuit which is coupled to a common cavity. The requisite frequency and phase relationship between the radio frequency oscillations of the different CW oscillators is determined in operation by the characteristics of the common cavity.
Although either of the combiner circuits shown by Kurokawa et al. and Harp et al. is satisfactory in its "steady state" condition, i.e. when producing CW oscillations, a somewhat different situation obtains when either is used to produce pulses of radio frequency energy. Pulsed design can be optimized for simultaneously achieving stability of operation, combining efficiency and spectral purity.
Another problem with pulsed IMPATT diode oscillators, not addressed in either of the cited patents, is that such devices require, for best operation, an electrical power supply which is effectively current-regulated in a particular manner. Specifically, the electrical power supply must, if the spectral purity of each pulse is to be maintained, be adapted to compensate for an increase in the temperature of the junction of the IMPATT diode during the generation of each pulse. In addition, when pulsed operation is desired, the rise and fall times of each pulse should be controllable to allow the spectrum of each radio frequency pulse to be shaped as desired.